(daily way in the model 0,46 m)
In many ways it is similar to its neighbouring planet Uranus. As the 8th planet seen from the sun it is the smallest and furthest gas planet. Its atmosphere, with winds reaching more than 1000 km/h, consists mainly of hydrogen. But there are also great parts of helium and traces of methane which, in frozen conditions, forms clouds. When the space probe Voyager flew past it in 1989, it observed a twirling "great dark spot", which was stable for a few months at least and reminded one of Jupiter's spot. The diameter of Neptune is 49.424 km, its average distance from the sun is 30,1 AU and its mass is 17 times that of the earth's. On its nearly circular orbit (only Venus has a less eccentric orbit), it moves once around the sun in 165 years and rotates, tilted at about 30° to the ecliptic pole, around its own axis in 16 hours. A mantle of ice surrounds a rocky core consisting of iron and silicates. This core is assumed to be considerably larger than Uranus` because Neptune, although with a smaller diameter, has a greater mass than its neighbouring planet. Neptune actually has an average temperature of -214° C and emits, in contrast to Uranus, much more energy (2,6 times more) than it receives from the sun. Its magnetic field is weaker than that of the other big planets, having a 47° slant towards the rotational axis like one has already seen with its neighbouring planet closer to the sun. Neptune has eight moons which are known about: 7 smaller ones of about 50 to 400 km in size and Triton, which has a diameter of 2700 km and can be compared to the earth's moon. This moon orbits the planet at a distance of 355.000 km retrogradely, which leads to the assumption that it is a captured asteroid. New pictures of Triton show signs of recent volcanic activity . Neptune also has a system of very weak rings, one of which has the shape of a plaited cord. In telescopes from earth in which Neptune appears as a tiny blue-green disc, the rings cannot be made out. Most of the recent findings about the gas giant are owed to the successful mission of Voyager 2, which passed it in August 1989 (three years after the probe's flight past Uranus) and to the Hubble Space Telescope (HST).
The history of its discovery sounds even more thrilling than
that of Uranus because there is the speculation that Galilei saw Neptune for a
short time during an observation of Jupiter in 1613, he identified and
described it, however, as a fixed star. More than 200 years later, the Briton
Adams and the Frenchman Leverrier calculated and discussed the irregularities of
Uranus` orbital path, during which they put the disturbances down to a planet
unknown at that time. During the search for it people also adopted the
Titius-Bode-Rule, more or less an accidental mathematical relation, which
describes the positional distances of the great planets in the solar system. And
they struck gold. An international competition concerning the new planet had
arisen in the meantime.
With the help of Leverrier`s calculations and exact celestial maps the German Galle, assisted by the Dane dŽArrest, searched from the Berlin observatory through the sky, when the assistant shouted, "This star is not on the map" - and thus Neptune was discovered in September 1846. Only a few weeks later the British Lassel found the Neptune moon Triton.
The planet owes its name - and this choice was heavily
disputed over for a long time - to the Roman god of the sea, whose Greek
equivalent is Poseidon. As the son of Kronos/Saturn and Rhea he is the elder
brother of Zeus/Jupiter. Neptun/Poseidon belongs to the most powerful gods.
Together with Jupiter and Mercury he is said to have been the creator of Orion. Neptune's symbol is a trident with a writhing fish on it. In Homer's epic poem "Odyssey" he determined the destiny of the heroes.